Galaxies 09: Assembly, Gas Content and Star Formation History of Galaxies
Dominik Riechers
Caltech
Molecular gas in high redshift galaxies
Detailed studies of the molecular gas content and dynamics in the highest redshift AGN host galaxies are vital for our understanding of the formation and evolution of massive galaxies. Molecular gas is the prerequisite material for star formation to occur. Also, gas dynamics can be used to trace the gravitational potential of galaxies, and thus, to obtain an independent estimate of the total mass in their central few kiloparsecs. This technique thus provides the possibility to set an upper limit on the gas fraction and stellar content of AGN host galaxies out to the earliest cosmic times, where direct observations of stellar light are not possible due to the brilliance of the AGN at optical/infrared wavelengths. Measuring the gas fraction is important to determine the evolutionary state of a galaxy, and to constrain gas depletion timescales and starburst lifetimes. Determining the stellar mass of distant galaxies is important to investigate whether or not the (in the nearby universe) linear relation between stellar mass and black hole mass in early-type galaxies evolves with cosmic time and/or toward the high mass end. Here, I present the results of a dynamical, high resolution (0.15 arcsec, or 1 kpc at $z>$4) study of molecular gas in quasar host galaxies out to $z$=6.4 (i.e., within 1 Gyr of the Big Bang) with the Very Large Array (VLA), which we performed to address these questions. These observations set the pace for future investigations of star formation and galaxy assembly out to the first galaxies that form in the universe, which will facilitate the capabilities of the upcoming Expanded Very Large Array (EVLA) and the Atacama Large (sub-)Millimeter Array (ALMA).
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